Soybean Cyst Nematode (SCN) is a parasitic pest which has threatened soybean production in the U.S. for more than fifty years. SCN resistance is an economically important trait as infection can substantially reduce yields. Despite this, two primary sources of resistance contribute to elite Pioneer germplasm: Peking and PI88788. Several loci have been reported to confer SCN resistance, arguably the most important of these rhg1 maps to linkage group G and is comprised of at least two alleles: rhg1 derived from Peking and rhg1-b derived from PI88788.
Cloning of the rhg1 allele was reported previously, and a candidate receptor-like kinase gene is the subject of a competitor's patent applications; despite this, no genetic evidence has been provided to support these claims. Furthermore, a recent study fine-mapped the rhg1-b allele to a 67-kb region which does not include the rhg1 candidate gene. In light of these reports, the true molecular nature of rhg1 and rhg1-b SCN resistant alleles remains unclear of the same gene and it is uncertain whether rhg1 and rhg1-b are alleles of the same resistant gene or represent two distinct albeit tightly linked genetic loci.
Molecular characterization of these alleles would have important implications for soybean cultivar improvement.